dlibs: make define_for_kernel work with kernels in any order

An undocumented requirement of define_for_kernel (and thus
expand_for_kernel) is that when multiple kernel versions are specified,
they must be in ascending order.  This is because __process_element does
not stop searching for an expansion when one is found, and doesn't check
to see if each expansion it finds is more suitable than any it already
knows about: so if you list an expansion for 5.11.0 followed by one for
4.10.0, and build it against 5.11.6, __process_element will conclude
(correctly) that 5.11.0 matches, mark it as found, then keep scanning,
conclude that 4.10.0 matches too, and overwrite the already-found match,
even though 5.11.0 is a better match for 5.11.6 than 4.10.0 is.

This is easy to fix: in addition to remembering the found match,
remember what version it matched against, and only overwrite matches if
the potential match has a higher version number.

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>

libdtrace/d-kern.m4

@@ -32,19 +32,22 @@ m4_define([[if_arch]],[[m4_ifelse(SUBST_ARCH,m4_quote($1),m4_quote($2))]])
  * details.
  */
 m4_define([[__process_element]], m4_dnl
-	[[m4_ifelse(m4_eval(SUBST_KERNEL[[ >= $1]]), 1, m4_dnl
-		[[m4_define([[__found]], [[$2]])]])]]) m4_dnl
+	[[m4_ifelse(m4_eval((SUBST_KERNEL[[ >= $1]]) && ($1 >= __found_version)), 1, m4_dnl
+		[[m4_define([[__found]], [[$2]]) m4_dnl
+		  m4_define([[__found_version]], [[$1]])]])]]) m4_dnl
 
 m4_define([[__cat]], [[$1$2]]) m4_dnl
 
 m4_define([[__define_for_kernel]], [[ m4_dnl
 	m4_pushdef([[__found]], nil) m4_dnl
+	m4_pushdef([[__found_version]], 0) m4_dnl
 	m4_foreachq(kernel, m4_quote($2), [[ m4_dnl
 		__cat([[__process_element]], kernel) m4_dnl
 	]]) m4_dnl
 	m4_ifelse(__found, nil, m4_dnl
 		[[m4_define(m4_quote($1), [[$3]])]], m4_dnl
 		[[m4_define(m4_quote($1), __found)]]) m4_dnl
+	m4_popdef([[__found_version]]) m4_dnl
 	m4_popdef([[__found]]) m4_dnl
 ]]) m4_dnl